It is known to perform the above processes on one or more textile yarns by passing the yarn or yarns through a jet device in which a jet or jets of air are directed transversely of the travelling yarn or yarns to agitate or twist the filaments or the fibres of the yarns. Agitation by such means may cause uniform texturing or intermittent texturing, i.e. intermingling or co-mingling. When intermittent, nips are produced in the yarn or yarns at spaced intervals. Since such jets rely on air turbulence, the degree of twist, texturing or of nip spacing along the yarn is in consequence random. Whilst the average degree of twist, texturing or nip production per unit length of yarn processed by such known jets may be satisfactory for certain textile applications, there are often long lengths of yarn produced having no twist, texture or nips. These lengths of yarn when used in knitted or woven fabrics manifest themselves as unsatisfactory regions in the fabric. To remove spin finish oil and to improve process stability it is known to wet the yarn prior to its entry into the air jet, but the above problems still exist. In addition, typically a machine for performing such processes can have many, for example 200 or more, processing positions, i.e. 200 or more yarns are processed simultaneously in parallel threadlines. The provision of high pressure air to such numbers of jets is expensive and such a machine is very noisy.